Isozyme data were used to identify populations of certain Lutzomyia taxa in the verrucarum species group, mostly in the series townsendi. Lutzomyia youngi Feliciangelis and Murillo and L. spinicrassa Morales, Osorno, Osorno, and Hoyos each have diagnostic allomorphs for phosphogluconate dehydrogenase (6PGDH) and fumarate hydratase (FUM). The 6PGDH and FUM data and those from 6-phospho-fructokinase and phosphoglucomutase distinguish Lutzomyia sp., a new species from Columbia to be described and named later. Data from these enzymes and glucose phosphate isomerase will separate L. townsendi (Ortiz) from the others and from L. longiflocosa Osorno, Morales, Osorno, and Hoyos, L. quasitownsendi Morales, Osorno, Osorno, and Hoyos, and L. sauroida Osorno, Morales, and Osorno (three species that are inseparable using enzyme data). Three other species, L. serrana (Damasceno and Arouck) (series serrana) and L. columbiana (Ristorcelli and Van Ty) and L. andina Osorno, Osorno, and Morales (both in series verrucarum), are morphologically distinct using conventional characters and have fixed diagnostic differences at several enzyme loci. Statistical analyses of the enzyme data using genetic identities (I), differences (D), and the amount of genetic variation among these taxa indicated that such statistics can be as useful in the study of sand fly phylogeny and population genetics as they have been for other organisms. I and D values indicated that L. longiflocosa, L. quasitownsendi, and L. sauroida are very similar (I = 0.991 and D = 0.010) and possibly are populations of the same conspecific species. The levels of divergence, based on combined enzyme data for up to 21 gene loci among the taxa, are discussed, and a dendrogram based on genetic distance is presented. The genetic data confirmed established phylogenetic relationships among the sand fly taxa based on structural similarities.